In a wireless communication system which uses multiple carriers, such as an orthogonal frequency division multiple access (OFDMA) or a single carrier-frequency division multiple access (SC-FDMA), radio resources are a set of continuous sub-carriers and are defined by a time-frequency region on a two-dimensional sphere. A time-frequency region is a rectangular form sectioned by time and sub-carrier coordinates. In other words, one time-frequency region could be a rectangular form sectioned by at least one symbol on a time axis and a plurality of sub-carriers on a frequency axis. Such a time-frequency region can be allocated to an uplink for a specific user equipment (UE), or a base station can transmit the time-frequency region to a specific user equipment in a downlink. In order to define such a time-frequency region on the two-dimensional sphere, the number of OFDM symbols and the number of continuous sub-carriers starting from a point having an offset from a reference point should be given.
An evolved universal mobile telecommunications system (E-UMTS) which is currently being discussed uses 10 ms radio frame comprising 10 sub-frames. Namely, one sub-frame includes two continuous slots. One slot has a length of 0.5 ms. Also, one sub-frame comprises a plurality of OFDM symbols, and a part (for example, first symbol) of the plurality of OFDM symbols can be used for transmission of L1/L2 control information.
FIG. 1 illustrates an example of a structure of physical channels used in the E-UMTS. In FIG. 1, one sub-frame comprises an L1/L2 control information transmission region (hatching part) and a data transmission region (non-hatching part).
FIG. 2 illustrates a general method of transmitting data in the E-UMTS. In the E-UMTS, a hybrid auto repeat request (HARQ) scheme, which is one of data retransmission schemes, is used to improve throughput, thereby enabling desirable communication.
Referring to FIG. 2, the base station transmits downlink scheduling information (hereinafter, referred to as ‘DL scheduling information’) through DL L1/L2 control channel, for example, a physical downlink control channel (PDCCH), to transmit data to a user equipment in accordance with the HARQ scheme. The DL scheduling information includes user equipment identifier (UE ID) or group identifier (group ID) of user equipments, location and duration (resource assignment and duration of assignment) information of radio resources allocated for transmission of downlink data, modulation mode, payload size, transmission parameters such as MIMO related information, HARQ process information, redundancy version, and new data indicator.
In order to notify that DL scheduling information is transmitted through the PDCCH for what user equipment, the user equipment identifier (or group identifier), for example, a radio network temporary identifier (RNTI) is transmitted. The RNTI can be classified into a dedicated RNTI and a common RNTI. The dedicated RNTI is used for data transmission and reception to and from a user equipment of which information is registered with a base station. The common RNTI is used if communication is performed with user equipments, which are not allocated with dedicated RNTI as their information is not registered with the base station. Alternatively, the common RNTI is used for transmission and reception of information used commonly for a plurality of user equipments, such as system information. For example, examples of the common RNTI include RA-RNTI and T-C-RNTI, which are used during a random access procedure through a random access channel (RACH). The user equipment identifier or group identifier can be transmitted in a type of CRC (Cyclic Redundancy Check) masking in DL scheduling information transmitted through the PDCCH.
User equipments located in a specific cell monitor the PDCCH through the L1/L2 control channel using their RNTI information, and receive DL scheduling information through the corresponding PDCCH if they successfully perform CRC decoding through their RNTI. The user equipments receive downlink data transmitted thereto through a physical downlink shared channel (PDSCH) indicated by the received DL scheduling information.
A scheduling mode can be classified into a dynamic scheduling mode and a persistent or semi-persistent scheduling mode. The dynamic scheduling mode is to transmit scheduling information to a specific user equipment through the PDCCH whenever allocation of uplink or downlink resources is required for the specific user equipment. The persistent scheduling mode means that the base station allocates downlink or uplink scheduling information to the user equipment statically during initial call establishment such as establishment of a radio bearer. In this document, the term of “persistent scheduling” has the same meaning with “semi-persistent scheduling.”
In case of the persistent scheduling, the user equipment transmits or receives data using scheduling information previously allocated to the base station without using DL scheduling information or UL scheduling allocated from the base station. For example, if the base station previously sets a specific user equipment to allow the user equipment to receive downlink data through RRC signal and a radio resource “A” in accordance with a transport format “B” and a period “C” during establishment of a radio bearer, the user equipment can receive downlink data transmitted from the base station using information “A”, “B” and “C”. Likewise, even in case that the user equipment transmits data to the base station, the user equipment can transmit uplink data using a previously defined radio resource in accordance with previously allocated uplink scheduling information. The persistent scheduling is a scheduling mode that can well be applied to a service of which traffic is regular, such as voice communication.
AMR codec used in voice communication, i.e., voice data generated through voice codec has a special feature. Namely, voice data are classified into a talk spurt and a silent period. The talk spurt means a voice data period generated while a person is actually talking, and the silent period means a voice data period generated while a person does not talk. For example, voice packets, which include voice data in the talk spurt, are generated per 20 ms, and silent packets (SID), which include voice data in the silent period, are generated per 160 ms.
If the persistent scheduling is used for voice communication, the base station will establish radio resources in accordance with the talk spurt. Namely, the base station will previously establish radio resources for transmitting and receiving uplink or downlink data to and from the user equipment at an interval of 20 ms during call establishment using a feature that voice packets are generated per 20 ms. The user equipment receives downlink data or transmits uplink data using radio resources, which are previously established per 20 ms.